Thrust bearing

ABSTRACT

In a thrust bearing ( 1 ) supporting a load in a thrust direction in a rotary portion, a size of a curved surface ( 32 ) in the forward side of a lubricating groove ( 3 ) with respect to a relative rotating direction (S) of an opposing sliding member is set to be larger than a size of a curved surface ( 31 ) in the rearward side of the lubricating groove ( 3 ) with respect to the relative rotating direction (S), and a depth (d1) of the lubricating groove ( 3 ) is set to be deeper than a starting point ( 32   a ) in the side of a groove bottom ( 33 ) of the curved surface ( 32 ) formed in the groove shoulder in the forward side of the lubricating groove ( 3 ) with respect to the rotating direction (S), so that a lubricating effect and a cooling effect are increased.

TECHNICAL FIELD

[0001] The present invention relates to a thrust bearing which supportsa load in the thrust direction in a rotation portion.

BACKGROUND ART

[0002] A stator of a torque converter in an automatic transmission of amotor vehicle can rotate only in one direction by a one-way clutch, anda thrust load applied to the stator is supported by a thrust bearing. Inthe thrust bearing of the torque converter, a low friction is requiredfor the purpose of reducing a loss of power energy transmission under ahigh speed driving condition so as to improve a specific fuelconsumption. Accordingly, as this kind of thrust bearing, there has beenemployed a needle bearing, or a copper washer or the like. However,since the needle bearing and the copper washer are expensive, needs fora synthetic resin thrust bearing which can be inexpensively manufacturedhave been increased in recent years.

[0003]FIGS. 13A and 13B a synthetic resin thrust bearing in accordancewith a conventional art which is used in a torque converter or the like,in which FIG. 13A is a front view as seen from the side of a slidingsurface, and FIG. 13B is a partly enlarged cross sectional view cutalong a line XIII-XIII in FIG. 13A. As shown in the figures, in thiskind of synthetic resin thrust bearing 100, a lot of lubricating grooves102 extending in the radial direction are formed on a sliding surface101 at a predetermined interval in the circumferential direction. Eachof the lubricating grooves 102 is provided so as to supply a lubricatingoil to the sliding surface 101, and groove shoulders 102 a and 102 b inboth sides are formed as curved surfaces or chamfer portions having thesame size.

[0004] However, in the conventional synthetic resin thrust bearing 100shown in FIGS. 13A and 13B, since the lubricating oil introduced intothe lubricating grooves 102 is hard to be sufficiently supplied to thelubricating surface 101, and further, since a depth d of the lubricatinggrooves 102 is shallow, a cooling effect achieved by the lubricating oilintroduced into the lubricating grooves 102 is not sufficient.Furthermore, because of the above insufficiency, there have been pointedout problems such that a friction with an opposing sliding member ishigh, a performance of the torque converter is lowered, and the specificfuel consumption is increased.

[0005] The present invention is made by taking the problems mentionedabove into consideration, and a technical object of the presentinvention is to provide a thrust bearing supporting a thrust load of arotation portion, in which a friction with an opposing sliding membercan be sufficiently lowered even when the thrust bearing is made of asynthetic resin.

DISCLOSURE OF THE INVENTION

[0006] As a means for effectively achieving the technical objectmentioned above, in accordance with a first aspect of the presentinvention, there is provided a thrust bearing comprising:

[0007] a lot of lubricating grooves formed on a sliding surface at apredetermined interval in the circumferential direction; and

[0008] curved surfaces formed in groove shoulders of each of thelubricating grooves,

[0009] wherein a size of the curved surface in the forward side of thelubricating groove with respect to a relative rotating direction of anopposing sliding member is set to be larger than a size of the curvedsurface, or the chamfer portion in place thereof, in the rearward sideof the lubricating groove with respect to the relative rotatingdirection.

[0010] In accordance with a second aspect of the present invention,there is provided thrust bearing as recited in the first aspect, whereina depth of the lubricating groove is set to be deeper than a startingpoint in the side of a groove bottom of the curved surface formed in thegroove shoulder in the forward side of the lubricating groove withrespect to the rotating direction.

[0011] In accordance with a third aspect of- the present invention,there is provided a thrust bearing as recited in the first aspect or thesecond aspect, wherein a step portion for enlarging a groove widthtoward the curved surface in the same side groove shoulder is formed inthe forward side of the lubricating groove with respect to the relativerotating direction of the opposing sliding member.

[0012] In accordance with a fourth aspect of the present invention,there is provided a thrust bearing as recited in the first aspect or thesecond aspect, wherein a groove inner wall in the forward side of thelubricating groove with respect to the relative rotating direction ofthe opposing sliding member is inclined such that the groove width isenlarged toward the curved surface in the same side groove shoulder.

[0013] In accordance with a fifth aspect of the present invention, thereis provided a thrust bearing as recited in any one of the first aspectto the fourth aspect, wherein a depth of the groove bottom of thelubricating groove is made gradually shallower from an end portion inthe inner peripheral side toward an end portion in the outer peripheralside.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIGS. 1A and 1B show a first embodiment of a thrust bearing inaccordance with the present invention, in which FIG. 1A is a front viewas seen from the side of a sliding surface, and FIG. 1B is a partlyenlarged cross sectional view cut along a line I-I in FIG. 1A;

[0015]FIG. 2 is a back view showing the first embodiment of the thrustbearing in accordance with the present invention;

[0016]FIG. 3 is a cross sectional view cut along a line III-O-III inFIG. 1A;

[0017]FIGS. 4A and 4B show an operation of a lubricating groove inaccordance with the present invention in comparison with an operation ofthe lubricating groove in accordance with the conventional art, in whichFIG. 4A is an explanatory view of the operation in accordance with thepresent invention, and FIG. 4B is an explanatory view of the operationin accordance with the conventional art;

[0018]FIG. 5 is a perspective view showing the operation of thelubricating groove in accordance with the present invention;

[0019]FIG. 6 is an explanatory chart showing a result obtained bymeasuring a change of friction coefficient by thrust loads to the thrustbearing in accordance with the present invention and the thrust bearingin accordance with the conventional art;

[0020]FIGS. 7A and 7B show a second embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 7A is a front viewas seen from the side of a sliding surface, and FIG. 7B is a partlyenlarged cross sectional view cut along a line VII-VII in FIG. 7A;

[0021]FIGS. 8A and 8B show a third embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 8A is a front viewas seen front the side of a sliding surface, and FIG. 8B is a partlyenlarged cross sectional view cut along a line VIII-VIII in FIG. 8A;

[0022]FIGS. 9A and 9B show a fourth embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 9A is a front viewas seen from the side of a sliding surface, and FIG. 9B is a partlyenlarged cross sectional view cut along a line IX-IX in FIG. 9A;

[0023]FIGS. 10A and 10B show a fifth embodiment of the thrust bearing inaccordance with the present invention, in which FIG. 10A is a front viewas seen from a side of a sliding surface, and FIG. 10B is a partlyenlarged cross sectional view cut along a line X-X in FIG. 10A;

[0024]FIG. 11 is a partly perspective view showing a sixth embodiment ofthe thrust bearing in accordance with the present invention;

[0025]FIG. 12 is a partly perspective view showing a seventh embodimentof the thrust bearing in accordance with the present invention; and

[0026]FIGS. 13A and 13B show a synthetic resin thrust bearing inaccordance with the conventional art, in which FIG. 13A is a front viewas seen from the side of a sliding surface, and FIG. 13B is a partlyenlarged cross sectional view cut along a line XIII-XIII in FIG. 13A.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027]FIGS. 1A and 1B show a thrust bearing in accordance with a firstembodiment, in which FIG. 1A is a front view as seen from the side of asliding surface, and FIG. 1B is a partly enlarged cross sectional viewcut along a line I-I in FIG. 1A, FIG. 2 is a back view of the samethrust bearing, and FIG. 3 is a cross sectional view cut along a lineIII-O-III in FIG. 1A.

[0028] A thrust bearing 1 in accordance with the present embodiment ismade of a synthetic resin and formed in a flat annular shape, and isstructured such as to support a thrust load of a rotation memberrotating only in one direction, for example, a stator of a torqueconverter in an automatic transmission of a motor vehicle. The thrustbearing 1 is structured such that one end surface in the axial directionforms a sliding surface 2 with an opposing sliding member, and a lot oflubricating grooves 3 extending in the radial direction are formed onthe sliding surface 2 at a predetermined interval in the circumferentialdirection.

[0029] In each of the lubricating groove 3, a groove width W1 is set,for example, about 1.4 mm, and curved surfaces 31 and 32 havingdifferent sizes are formed in groove shoulders arranged in both sides ofthe lubricating groove 3. In particular, a relatively small first curvedsurface 31 is formed in the groove shoulder in the rearward side of thelubricating groove 3 with respect to a relative rotating direction S ofan opposing sliding member facing to the sliding surface 2, among thegroove shoulders in both sides of the lubricating groove 3, and a radiusR1 of curvature of the first curved surface 31 is set to be 0.5 mm orless. Further, a relatively large second curved surface 32 is formed inthe groove shoulder in the forward side of the lubricating groove 3 withrespect to the relative rotating direction S of the opposing slidingmember, and a radius R2 of curvature of the second curved surface 32 isset to be substantially larger than the radius R1 of curvature of thefirst curved surface 31. In the present embodiment, the radius R1 ofcurvature of the first curved surface 31 is formed, for example, about0.3 mm, and the radius R2 of curvature of the second curved surface 32is formed, for example, about 2 mm.

[0030] A depth d1 of a groove bottom 33 in each of the lubricatinggrooves 3 is formed deeper than a starting point 32 a in the side of thegroove bottom 33 in the second-curved-surface 32. In the presentembodiment, a depth d2 of the starting point 32 a with respect to thesliding surface 2 is, for example, about 0.7 mm, and the depth d1 of thegroove bottom 33 is deeper than it and, for example, about 1.95 mm.

[0031] Further, an angle θ of a groove inner wall in the rearward sideof the lubricating groove 3 with respect to the relative rotatingdirection S of the opposing sliding member, that is, a groove inner wall34 in the side of the first curved surface 31 forms an angle between 80and 90 degrees toward the opposite side to the rotating direction S,with respect to the sliding surface 2, preferably forms an angle of 90degrees with respect to the sliding surface 2. Further, a width L in theperipheral direction of the sliding surface 2 is set to be, for example,about 6 mm in a center portion in the radial direction.

[0032]FIGS. 4A and 4B are explanatory views showing comparatively anoperation of the lubricating groove 3 in accordance with the presentembodiment and an operation of the lubricating groove in accordance withthe conventional art, and FIG. 5 is a perspective view showing theoperation of the lubricating groove 3 in accordance with the presentembodiment. The thrust bearing 1 in accordance with the presentembodiment is structured, as shown in FIG. 4A, such that when theopposing sliding member 4 facing to the sliding surface 2 of the thrustbearing 1 in the thrust direction relatively rotates in the direction ofan arrow S, in other words, the counterclockwise direction in FIG. 1A, alubricating oil O introduced into the lubricating groove 3 runs over thesliding surface 2 from the second curved surface 32 in the forward sideof the lubricating groove 3 with respect to the rotating direction S insuch a manner that the lubricating oil O is drawn in by the opposingsliding member 4. Since the radius R2 of curvature and the depth of thestarting point 32 a of the second curved surface 32 is larger than theradius R1 of curvature of the first curved surface 31, the lubricatingoil O tends to interpose into a sliding gap δ between the slidingsurface 2 and the opposing sliding member 4 from the lubricating groove3, and consequently, a wedge effect of the lubricating oil O isincreased in accordance with the structure that the gap is reduced withrespect to the relative rotating direction S of the opposing slidingmember 4, whereby an effective bearing pressure P is generated.

[0033] On the other hand, since the first curved surface 31 in theopposite side to the second curved surface 32 is structured such as toenlarge the gap with respect to the relative rotating direction S of theopposing sliding member 4, a reverse wedge effect of drawing out alubricating oil film from the sliding gap δ between the sliding surface2 and the opposing sliding member 4 is generated in correspondence tothe sliding motion of the opposing sliding member 4. However, since theradius R1 of curvature of the first curved surface 31 is substantiallysmall in comparison with the radius, R2 of curvature of the secondcurved surface 32, the reverse wedge effect achieved by the first curvedsurface 31 is small in comparison with the wedge effect achieved by thesecond curved surface 32. In particular, when the radius R1 of curvatureof the first curved surface 31 is set to be 0.5 mm or less, the reverewedge effect is hardly generated.

[0034] Further, when the angle θ of the groove inner wall 34 in the sideof the first curved surface 31 is small, the reverse wedge effect isgenerated thereby. However, since the angle θ is approximately 90degrees. in the present embodiment, the reverse wedge effect caused bythe groove inner wall 34 is hardly generated.

[0035] On the contrary, in the thrust bearing 100 in accordance with theconventional art shown in FIG. 4B, a groove shoulder 102 b causinggeneration of the bearing pressure P on the basis of the wedge effect inthe forward side of a lubricating groove 102 with respect to therotating direction S, and a groove shoulder 102 a causing generation ofthe reverse wedge effect in the rearward side of the lubricating groove102 are formed so as to have the same radius of curvature with eachother. Accordingly, the wedge effect achieved by the curved surface 102b is cancelled by the reverse wedge effect achieved by the curvedsurface 102 a, so that the bearing pressure P can not be enlarged.

[0036] Thus, on the basis of the thrust bearing 1 in accordance with thepresent embodiment, it is possible to obtain a remarkable bearingpressure P for expanding the sliding gap δ. Accordingly, even when thethrust bearing 1 is made of the synthetic resin, a friction between theopposing sliding member 4 and the sliding surface 2 is reduced, and itis possible to effectively reduce a loss of power energy. Further, it istherefore possible to improve a performance of the torque converter andit is possible to improve the specific fuel consumption.

[0037] Further, in the thrust bearing 100 in accordance with theconventional art shown in FIG. 4B, since a groove bottom 102 c iscontinuous from the curved surfaces of the groove shoulders 102 a and102 b, a groove depth d0 is shallow and is about 0.5 mm, so that thelubricating oil is less flown within the lubricating groove 102.

[0038] On the other hand, in the present embodiment, the depth d1 of thegroove bottom 33 in the lubricating groove 3 is deeper than the startingpoint 32 a in the side of the groove bottom 33 in the second curvedsurface 32, and the angle θ of the groove inner wall 34 in the rearwardside of the lubricating groove 3 with respect to the rotating directionS forms the angle between 80 and 90 degrees toward the opposite side tothe rotating direction S with respect to the sliding surface 2.Accordingly, a negative pressure portion n is generated near the grooveinner wall 34 within the lubricating groove 3. Further, as describedabove, since the reverse wedge effect of drawing out the lubricating oilfilm from the sliding gap δ is small in the first curved surface 31, thelubricating oil O is supplied to the negative pressure portion n notfrom the sliding gap δ but from both ends 3 a and 3 b in the radialdirection of the lubricating groove 3 in major part, as shown in FIG. 5.In particular, since a centrifugal force is applied to the lubricatingoil, the lubricating oil is introduced into the lubricating groove 3mainly from the inner peripheral side of the thrust bearing 1 (the endportion 3 a of the lubricating groove 3).

[0039] Therefore, since the lubricating oil can be actively flownbetween the inner and outer peripheries of the thrust bearing 1 and thelubricating groove 3, it is possible to increase a cooling effect of thesliding portion. Further, since the thick lubricating oil film is keptin the sliding gap 6 as the result, it is possible to reduce a frictionbetween the opposing sliding member 4 and the sliding surface 2.

[0040]FIG. 6 shows a result obtained by measuring a change of frictioncoefficient caused by thrust loads in the thrust bearing in accordancewith the present embodiment and the thrust bearing in accordance withthe conventional art. On the basis of the test result, it is confirmedthat the thrust bearing in accordance with the present embodiment isindicative of a low friction and stable bearing performance, while thethrust bearing in accordance with the conventional art is indicative ofa rapid increase of the friction coefficient even under the small thrustloads. Further, it is known that the thrust bearing in accordance withthe present embodiment maintains a comparatively low frictioncoefficient owing to a sufficient cooling effect of the lubricating oil,even in the case that the thrust bearing is reverse rotated, that is,the relative rotating direction of the opposing sliding member is set tothe opposite direction to the arrow S in FIG. 4B.

[0041]FIGS. 7A and 7B show a thrust bearing in accordance with a secondembodiment, in which FIG. 7A is a front view as seen from the side of asliding surface, and FIG. 7B is a partly enlarged cross sectional viewcut along a line VII-VII in FIG. 7A. The thrust bearing 1 in accordancewith this embodiment is employed in a structure in which the opposingsliding member relatively rotates in the reverse direction to that inFIGS. 1A and 1B, that is, in a clockwise direction in FIG. 7A. A crosssectional shape of each of the lubricating grooves 3 is formed in asymmetrical cross sectional shape to that of FIG. 1B described above,with respect to a circumferential direction. Accordingly, the sameoperation and effect as those of the first embodiment can be achieved.

[0042]FIGS. 8A and 8B show a thrust bearing in accordance with a thirdembodiment of the present invention, in which FIG. 8A is a front view asseen from the side of a sliding surface, and FIG. 8B is a partlyenlarged cross sectional view cut along a line VIII-VIII in FIG. 8A. Thepresent embodiment is structured such that a step portion 37 having adepth d3 is formed in the forward-side with respect to the relativerotating direction S of the opposing sliding member. Further, in thesame manner as that in FIGS. 1A and 1B, the first curved surface 31having the radius R1 of curvature of 0.5 mm or less is formed in thegroove shoulder in the rearward side with respect to the relativerotating direction S of the opposing sliding member, and the secondcurved surface 32 having the radius R2 of curvature which issubstantially larger than the radius R1 is formed in the groove shoulderin the forward side. Further, a groove width W2 between the groove innerwall 34 and the step portion 37 is set to be about a half of a groovewidth W1 between the groove inner wall 34 and the rising portion of thestep portion 37.

[0043] Therefore, in accordance with the present embodiment, since thelubricating oil introduced into the lubricating groove 3 is introducedinto the sliding surface 2 from the second curved surface 32 via thestep portion 37, the lubricating oil is further easily interposed in thesliding gap, and an improved bearing effect can be obtained. In thiscase, the step portion 37 may be formed, in the same manner, in thestructure in which a chamfer portion is formed in place of the firstcurved surface 31.

[0044]FIGS. 9A and 9B show a thrust bearing in accordance with a fourthembodiment of the present invention, in which FIG. 9A is a front view asseen from the side of a sliding surface, and FIG. 9B is a partlyenlarged cross sectional view cut along a line IX-IX in FIG. 9A. Thepresent embodiment is structured such that a chamfer portion 37 a isformed in a shoulder portion of the step portion 37 in accordance withthe third embodiment shown in FIGS. 8A and 8B mentioned above. The otherstructures are the same as those in FIGS. 8A and 8B. Accordingly, in thesame manner as the embodiment shown in FIGS. 8A and 8B, the lubricatingoil well runs over the step portion 37 from the side of the groovebottom 33, so that an improved bearing effect can be obtained.

[0045] In this case, in FIGS. 8A, 8B, 9A and 9B, only one step portion37 is formed, however, plural stages of step portions having differentdepths may be formed in such a manner as to be made shallower step bystep toward the second curved surface 32.

[0046]FIGS. 10A and 10B show a thrust bearing in accordance with a fifthembodiment of the present invention, in which FIG. 10A is a front viewas seen from the side of a sliding surface, and FIG. 10B is a partlyenlarged cross sectional view cut along a line X-X in FIG. 10A. Thepresent embodiment is structured such that a groove inner wall in theforward side with respect to the relative rotating direction S of theopposing sliding member, that is, a groove inner wall 38 in the side ofthe second curved surface 32 is inclined at an angle θ1. Further, agroove width W3 of the groove bottom 33 is set to be about a half of thegroove width W1 between the groove inner wall 34 and a starting point 32a in the side of the groove bottom 33 of the second curved surface 32.The other structures are the same as those in FIGS. 1A and 1B.

[0047] In accordance with the present embodiment, the sliding surface 2of the thrust bearing 1 and the opposing sliding member facing to thesliding surface 2 in the thrust direction relatively rotate in thedirection of the arrow S. Accordingly, the lubricating oil introducedinto the lubricating groove 3 is introduced onto the sliding surface 2from the second curved surface 32 in the forward side of the lubricatinggroove 3 with respect to the rotating direction S in such a manner thatthe lubricating oil is drawn in by the opposing sliding member, and thelubricating oil runs over the side of the second curved surface 32 fromthe groove bottom 33 so as to supplement it. In this structure, the flowof the lubricating oil becomes smoother than the case that the grooveinner wall 38 is vertical to the sliding surface 2. Therefore, thelubricating oil is further easily interposed in the sliding gap, and animproved bearing effect can be obtained. In this case, the inclinedgroove inner wall 38 may be applied, in the same manner, to thestructure in which the chamfer portion as shown in FIGS. 8A and 8B isformed in place of the first curved surface 31. the inclined grooveinner wall 38 may be applied, in the same manner, to the structure inwhich the first chamfer portion 35 and the second chamfer portion 36 asshown in FIGS. 8A and 8B are formed.

[0048]FIG. 11 is a partly perspective view showing a thrust bearing inaccordance with a sixth embodiment of the present invention. In thepresent embodiment, the groove bottom 33 of each of the lubricatinggrooves 3 is formed so as to be made shallower gradually from the endportion 3 a in the inner peripheral side of the thrust bearing 1 towardthe end portion 3 b in the outer peripheral side. A cross sectionalshape of a center portion in a longitudinal direction of each of thelubricating grooves 3 is the same as that in FIG. 1B described above,that is, the first curved surface 31 having the radius of curvature of0.5 mm or less is formed in the groove shoulder in the rearward side ofthe lubricating groove 3 with respect to the relative rotating directionS of the opposing sliding member to the sliding surface 2, and thesecond curved surface 32 having the radius of curvature which issubstantially larger than that of the first curved surface 31 is formedin the groove shoulder in the forward side. Further, the depth d1 of thegroove bottom 33 is deeper than the depth of the starting point 32 a inthe side of the groove bottom 33 in the second curved surface 32, at theend portion 3 a in the inner peripheral side of the thrust bearing 1,and is similar to the depth d2 at the end portion 3 b in the outerperipheral side. The other structures are the same as that in FIGS. 1Aand 1B.

[0049] The opposing sliding member relatively rotates in the directionof the arrow S, whereby the centrifugal force is applied to thelubricating oil O existing on the periphery thereof. Accordingly, thelubricating oil O is introduced into the lubricating groove 3 from theinner peripheral side of the thrust bearing 1, that is, from the endportion 3 a. At this time, in accordance with the embodiment shown inFIGS. 8A and 8B, since the groove bottom 33 becomes shallower inaccordance with the movement of the lubricating oil O toward the outerperipheral side of the thrust bearing 1 within the lubricating groove 3,the lubricating oil O is efficiently introduced onto the sliding surface2 from the second curved surface 32. Further, since the diminishingpassage in which the cross sectional area is reduced gradually towardthe outer peripheral side is formed between the lubricating groove 3 andthe opposing sliding member, the lubricating oil O is pressurized in theprocess of moving toward the outer peripheral side of the thrust bearing1 within the passage (the lubricating groove 3) on the basis of thecentrifugal force. Accordingly, the bearing pressure is increased and animproved bearing effect can be obtained.

[0050]FIG. 12 is a partly perspective view showing a thrust bearing inaccordance with an seventh embodiment of the present invention. Thepresent embodiment corresponds to a structure in which the structure inFIG. 11 is applied to the embodiment shown in FIG. 8A and 8B mentionedabove. In the present embodiment, the depth d1 of the groove bottom 33is deeper than the step portion 37 at the end portion 3 a at the innerperipheral side of the thrust bearing 1, and is similar to the depth ofthe step portion 37 at the end portion 3 b in the outer peripheral side.Accordingly, in the same manner as that in FIG. 11, the groove bottom 33is made shallower in accordance with the movement of the lubricating oilO toward the outer peripheral side of the thrust bearing 1 within thelubricating groove 3. Thus, the lubricating oil O is efficientlyintroduced onto the sliding surface 2 from the step portion 37 via thesecond curved surface 32, and is pressurized. Therefore, the bearingpressure is increased, and an improved bearing effect can be obtained.

[0051] Further, in each of the embodiments shown in FIGS. 9A, 9B, 10Aand 10B, the structure may be made, in the same manner, such that thegroove bottom 33 is made shallower gradually from the end portion in theinner peripheral side of the thrust bearing 1 toward the end portion inthe outer peripheral side, whereby it is possible to further improve thebearing effect.

[0052] Further, in each of the embodiments in FIGS. 8A and 8B to FIG.12, each of the lubricating grooves 3 may be formed in a symmetricalcross sectional shape with the illustrated shape, in correspondence tothe relative sliding direction of the opposing sliding member.

[0053] In this case, the thrust bearing 1 in accordance with the presentinvention is not limited to the bearing means of the stator of thetorque converter in the automatic transmission of the motor vehicle, andis useful for a thrust bearing of the other rotary equipment.

INDUSTRIAL APPLICABILITY

[0054] As described above, in accordance with the thrust bearing on thebasis of the first aspect of the present invention, the curved surfacewhich is larger than the size of the curved surface or the chamferportion in the rearward side of the lubricating groove is formed in thegroove shoulder in the forward side of the lubricating groove withrespect to the relative rotating direction of the opposing slidingmember. Thus, in the forward side of or the chamfer portion thelubricating groove, the lubricating oil tends to interpose into thesliding gap between the sliding surface and the opposing sliding memberand the wedge effect of the lubricating oil is enlarged, and in therearward side of the lubricating groove, the reverse wedge effectbecomes significantly small. Therefore, it is possible to sufficientlyreduce the friction with the opposing sliding member even in the casethat the thrust bearing is made of the synthetic resin, and it ispossible to provide a thrust bearing which is inexpensive and has anexcellent bearing performance.

[0055] In accordance with the thrust bearing on the basis of the secondaspect of the present invention, the depth of the lubricating groove isset to be deeper than the starting point in the side of the groovebottom of the curved surface or the chamfer portion formed in the grooveshoulder in the forward side of the lubricating groove with respect tothe rotating direction. Accordingly, the major part of the lubricatingoil is supplied to the lubricating groove from both ends in the radialdirection of the lubricating groove, and the lubricating oil is activelyflown between the inner and outer peripheries of the thrust bearing andthe lubricating groove, so that the cooling effect of the lubricatingportion can be increased. Therefore, in this case, it is possible toachieve the reduction of friction by the thick lubricating film.

[0056] In accordance with the thrust bearing on the basis of the thirdaspect of the present invention, the step portion is formed in theforward side of the lubricating groove with respect to the relativerotating direction, of the opposing sliding member. Accordingly, it ispossible to further increase the effects obtained by the first aspect orthe second aspect of the present invention.

[0057] In accordance with the thrust bearing on the basis of the fourthaspect of the present invention, the groove inner wall in the forwardside of the lubricating groove with respect to the relative rotatingdirection of the opposing sliding member is inclined. Accordingly, it ispossible to further increase the effects obtained by the first aspect orthe second aspect of the present invention.

[0058] In accordance with the thrust bearing on the basis of the fifthaspect of the present invention, the depth of the groove bottom of thelubricating groove is made shallower gradually from the end portion inthe inner peripheral side toward the end portion in the outer peripheralside. Accordingly, the lubricating oil can be efficiently interposedinto the sliding gap between the sliding surface and the opposingsliding member, and the lubricating oil moving to the outer peripheralside within the groove is pressurized by the centrifugal force, wherebythe bearing pressure is increased. Therefore, it is possible to furtherincrease the effects obtained by the first aspect to the fourth aspectof the present invention.

What is claimed is:
 1. (Amended) A thrust bearing comprising: a lot oflubricating grooves (3) formed on a sliding surface (2) at apredetermined interval in the circumferential direction; and curvedsurfaces (31, 32) formed in groove shoulders of each of the lubricatinggrooves (3), wherein a size of the curved surface (32) in the forwardside of said lubricating groove (3) with respect to a relative rotatingdirection (S) of an opposing sliding member is set to be larger than asize of the curved surface (31) or the chamfer portion in a rearwardside of said lubricating groove (3) with respect to said relativerotating direction (S).
 2. A thrust bearing as claimed in claim 1,wherein a depth. (d1) of the lubricating groove (3) is set to be deeperthan a starting point (32 a) in the side of a groove bottom (33) of thecurved surface (32) formed in the groove shoulder in the forward side ofthe lubricating groove (3) with respect to the rotating direction (S).3. A thrust bearing as claimed in claim 1 or 2, wherein a step portion(37) for enlarging a groove width toward the curved surface (32) in thesame side groove shoulder is formed in the forward side of thelubricating groove (3) with respect to the relative rotating direction(S) of the opposing sliding member.
 4. A thrust bearing as claimed inclaim 1 or 2, wherein a groove inner wall (38) in the forward side ofthe lubricating groove (3) with respect to the relative rotatingdirection (S) of the opposing sliding member is inclined such that thegroove width is enlarged toward the curved surface (32) in the same sidegroove shoulder.
 5. A thrust bearing as claimed in any one of claims 1to 4, wherein a depth (d1) of the groove bottom (33) of the lubricatinggroove (3) is made gradually shallower from an end portion (3 a) in theinner peripheral side toward an end portion (3 b) in the outerperipheral side.